> “bzip3 is not yet listed on the large text compression benchmark” It is now
And it comes in relatively well, in my opinion. I'm a compression amateur, but bzip3 is the first entry I recognize as a general purpose compression program.
I was processing compressed .jsonl files recently (JSON lines format). I found that lzma gave a much better compression than gzip or bzip2, which helps for archival costs, but it's challenging to work with as software support is lacking. I do duckdb processing which supports gzip transparently. There's an extension for bzip2, but not for lzma or bzip3.
I ended up using gzip because it's best supported by the software I use and most likely to have support in software I adopt. But it gave the worst compression results of the options I tried. These bzip3 numbers certainly give me FOMO...
For that type of structured data (logs and such), a custom dictionary can be extremely effective. Zstd among others support generating a custom dictionary. You just run zstd --train over the data first, and then feed that in when you run zstd. For example: I found ~10 gigabytes of Usenet headers compress to ~700 MB using Zstd and 1 MB shared dictionary -- and that's with each header individually compressed, so o(1) lookup time.
Back in my data hoarder days, I downloaded one of those torrents that had all the world's books in it. It was dunno how many terabytes, but way more than I had HDDs.
So I stripped out formatting, got rid of dupes, and tried out zstd, which was the hot new thing, along with the dictionary feature you describe, figuring it'd help. It didn't. I tried having one per book, one per multiple books, one for the whole archive.
It didn't work, or the gains were so marginal that I ended up scrapping the approach.
So it's not impossible that it can work, but stuff like regular json already compresses extremely well, I haven't found a scenario where it's a major boon.
The thing zstd got really right is fast decompression. For write-once read-never data like backups lzma (aka xz/7zip/lzip) is great. But it takes forever to decompress. On zstd I can get good compression while decompressing the file only marginally slower than reading the uncompressed file from SSD
Writing your files directly into a compressed stream and decompressing on the fly has become almost a standard workflow for any files I'm going to read and write sequentially anyways. No need for the data to ever exist uncompressed on the file system. Previous formats never did that for me because they either had too much overhead or too little gain, often both
It isn't really the go-to compression format, because it isn't ubiquitous like gzip and zip, there are a variety of compression tools out there for different purposes, and there is image/audio/video compression. There is also specialized compression like what git does with its rolling hashes. I think of it as there not being a go-to compression format.
A go-to thing means it's a sensible default choice and has no little to no downsides (versus not using compression), it doesn't mean it's the best for everything.
Until now the go-to has been DEFLATE (gzip and zip) but zstd is definitely competing against it because it is better in almost every way.
The benchmarks are disingenuous, to the point of looking cherry-picked. The block size for bzip3 is set to 512MB, but the window size for zstd is left to its default (8MB I believe for high levels). So in this corpus, which is made up of all versions of Perl source code concatenated, the window is too small to see all the identical files and just match them.
Also corpora made out of very long repetitions are pretty much the best case scenario for BWT-based compressors.
If we match the window size of zstd to that of bzip3 we get dramatically different results:
% gzcat *.gz | time zstd -T8 -16 | wc -c # baseline
2819113884
zstd -T8 -16 2054.50s user 3.47s system 783% cpu 4:22.80 total
% gzcat *.gz | time zstd -T8 -16 --long=29 | wc -c
196405076
zstd -T8 -16 --long=29 1083.06s user 2.41s system 783% cpu 2:18.55 total
Almost 15x smaller than the baseline, and more than 2x smaller than bzip3, also CPU time halves (since long matches are found earlier, so there's less work to do).
(the baseline number is slightly different because I don't have the exact Perl version set used by the author)
Also, in the benchmarks using lrzip, which would make the window size less relevant, zstd is not even compared.
> That always seemed annoying to me. They couldn't allocate 5 more bits somewhere to let the decompressor autodetect longer window sizes?
I believe this is just to prevent the decompressor from arbitrarily blowing up memory usage based on the input; I think if you want to accept long windows you can just always decompress with --long=63 regardless of whether the input needs it? (you will run out of RAM decompressing a long=63 file though of course)
These command line parameters change the maximum the decompressor will allow. It's 128 MiB by default in the command line decompressor; other uses (like the "zstd" content coding for HTTP in web browsers) use a lower limit of 8 MiB (see https://www.rfc-editor.org/rfc/rfc9659.html).
2^27 is 128 megabytes. How much RAM do you want the decompressor to have to allocate for every file? Especially since you can't tell, by looking only at the file size of a compressed file, how many bytes it will decompress to. You could read the file header, but if it's a malicious "zip bomb" type of file, the header could be lying.
I just tried a tar file of a git clone of the linux kernel sources where the most recent commit is 72c395024dac5e215136cbff793455f065603b06 (early Feb of this year). zstd -19 got a slightly smaller size (3582930348 bytes vs bz3 -b 511's 3597411687 bytes or 0.4% advantage to zstd). More significantly 4-core zstd decompression was 2.05 seconds vs a whopping 297 seconds for bzip3 -dj4 - 145x or over 2 orders of magnitude slower (about as much time to decode as to encode in the first place). bzip3 1.5.3 compiled with gcc-16.1.0. Granted, the .git objects are all compressed already and uncompressed tar-ball was only 5426667520 bytes, but even so...A lot of people care about fast(-ish) decompression. Maybe I did something wrong? Maybe `rm -rf .git` first would be a better benchmark?
This was my point too, but related to LZMA(2?) / xz, as the exact parameters were not specified while it supports setting compression level up to -9e, and the dictionary size can be controlled directly as well (in addition to quite a lot of fine-tuning knobs), increasing it up to 1536 MiB.
Wow, that is widely disingenuous, I don't really think there is any excuse for that, I don't believe someone deep in compression algorithms wouldn't know they could adjust the block size, and 512GB is a huge block size for bzip3, as it needs to basically all be in memory so you can't pretend that's just 'the standard value'.
Can you tell me what the zstd invocation is that corresponds to the default invocation of bzip3, which uses block size 16 MiB (according to the man page)?
I got some really good results with bzip3 compression Wikipedia XML dumps, and I would like to check if it's actually better or if I was just calling zstd wrong.
If you want a 16MB window, use `--long=24` (2^24 is 16M). (I believe this is larger than the default window for zstd level 3, but smaller than the default window at higher compression levels.)
> However, the complexity of the algorithms, and, in particular, the presence of various special cases in the code which occur with very low but non-zero probability make it impossible to rule out the possibility of bugs remaining in the program.
Sounds like perhaps a nice testcase for formalization + AI?
imo, partially because it's still not easy (in terms of code -> formal proof). For AI -- I've been Lean-ifying a simpler (but non-trivial) algo. Pointing (current) AI at it only goes so far and in fact might go "too far" in certain cases, where a non-formalized argument would have sufficed. There's also "who watches the watcher" -- did it really prove what we're supposed to prove?
For something like these compression algos, though, I imagine it would be much easier since they already have actual proofs out there.
I think this should include benchmarks zstd with larger windows and long range mode. I wouldn't be surprised if the window they used is smaller than an individual version tar file, which would prevent useful compression.
It's distasteful to use such a name when it's not created by the bzip authors. For some reason open source developers love using would be trademark infringing names instead of coming up with something unique.
That's like comparing apples to pears. OpenZL is not general purpose. You specify a format for data and it compresses that format. Specifying a general "could be anything" format would be interesting, but I doubt it would compress as well.
This big warning gave me pause, too. Why not have a compression option that automatically checks the data after compression (by decompressing and checking against a hash of the original data), which would reduce the probability of undetected errors to that of a hash collision? i.e. like `7z a` followed by `7z t`, but in one command.
Is that all that different than the standard MIT License:
> THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE....
Practically, no. But that specific disclaimer could lead on to think that there may have been some observed data corruption in practice that isn't disclosed. I have no idea if there is, but I'm not keen to discover it myself.
Also practically, this isn't MIT. It is LGPL 3, which I believe includes the warranty terms of GPL 3, i.e., no warranty. So we're in the same place anyway.
Depends - if parallel decompression of any bzip3 archive is possible I'd consider it fair, if it requires special flags on archive creation I'd consider it unfair. I didn't see any description about that on that page.
pbzip2 only can do parallel decompression on archives created with pbzip2, otherwise it'll fall back to single thread. There nowadays seems to be lbzip2, though, which claims to be able to add SMP support for standard bzip2 archives.
I'll need to try that next time I'm working with large archives - I learned about the pbzip2 limitations the hard way last time I was shuffling around a few multi-10GB archives, and was trying to speed things up fully utilising my 32 core threadripper.
It's a very strange algorithm completely different from most compression methods, that's what makes it interesting IMO. But it's probably not realistically competitive, since one needs to do more after the burrows-wheeler transform, and all that "more" has been ridiculously more optimized in zstd and other modern compression methods. Compressing bwt-transformed data is easier, but that doesn't mean it's easy to further than what's easy.
I have not experimented with bzip3 recently, but more than a year ago I have done many tests with it.
Initially I was extremely impressed with it, because in a lot of tests it succeeded to compress hard-to-compress files, like movies, and in many cases it demonstrated a much better compromise between speed and compression ratio than zstd, i.e. depending on the command parameters I could make it either compress better than zstd at similar compression/decompression speed, or compress/decompress faster at a similar compression ratio.
Alas, the initial extremely favorable conclusion was short-lived, because trying later bzip3 on other data files gave worse results than zstd.
So the final conclusion was that the performance of bzip3 was somewhat unpredictable, being highly data dependent. For some files it provided outstanding compression ratio or speed, but for others it was inferior.
The problem was that without doing a compression there was no way to guess whether a file would be among those preferred by bzip3 or by zstd or by xz.
So now I would use it only for a file for which I want maximum compression and which I would compress once and decompress many times, so I can afford a very long compression time, during which I would test multiple compression algorithms, including bzip3 and zstd, with multiple parameter choices, and I would eventually choose the one that offers the best compromise between compression ratio and decompression time, for that particular file.
It certainly is a competitive compression algorithm, but unless it has changed since I last tested it, you cannot guess for which files it would win the compression competition.
Would a multi-stream archive format make sense at this point? I.e. store several compressed streams in the same file and use heuristics to decide where each file (or portion of file) goes.
But developing the heuristics for choosing the appropriate compression algorithm for a stream of data is likely to need a very long time for compression tests of a lot of diverse training data, similarly to the training of a specialized ML model that classifies patterns.
Such heuristics should provide not only algorithm selection, but also parameter selection, when given only some simple input, e.g. the relative importances of compression ratio, decompression speed and compression speed.
There is a comparison with "zstd -19" on the Silesia corpus, showing better compression ratio for bzip3 (47.2 vs 53MB) while being ~5 times faster (and using only half the memory).
Even if the examples are highly cherry-picked, it is quite suprising to me that such pareto-dominance is possible at all.
edit: Tested it myself and found that it often also does slightly worse than zstd -19 in compression ratio but faster (it was slower in one case on "uncompressible" input).
Compression performance vs "zstd -19" seems to depends a lot on actual input data in a very unpredictable way. I'd assume the benchmarks that they show are definitely somewhat cherry-picked.
having used zstd, it has terrible defaults, optimized for speed and low-memory. You need to change it's params (not just level and dict size) to get high performance.
probably somebody should use a coding agent to do auto-research to optimize params for each compression algo, while matching one fixed goal - time, memory or size
The benchmark is very rudimentary. It does not test different levels/settings apart from its own -b 256/512 (does it affect decompression?), it doesn't measure compression time and memory usage. It does not specify parallel vs single-threaded (it mentions parallel on the one decoding number but what about the others?).
The lrzip test is interesting but it omits for example zstd and doesn't even have (de-)compression timings.
A lot more numbers are needed to present a fair and informative comparison.
I don't want this to be a swipe against bzip3, I only want to point out the presented benchmarks could be a lot better.
Previously:
“Hi, tool author here.” A useful explanation of Burrows-Wheelers transform as used by bzip3: https://news.ycombinator.com/item?id=42902407
“bzip3 is not yet listed on the large text compression benchmark” It is now: https://mattmahoney.net/dc/text.html
(2 years ago, 176 comments) https://news.ycombinator.com/item?id=42899713
(4 years ago, 104 comments) https://news.ycombinator.com/item?id=31324439
> “bzip3 is not yet listed on the large text compression benchmark” It is now
And it comes in relatively well, in my opinion. I'm a compression amateur, but bzip3 is the first entry I recognize as a general purpose compression program.
> “Hi, tool author here.” A useful explanation of Burrows-Wheelers transform as used by bzip3
FWIW, the Burrows-Wheelers transform is also used by bzip2, so this isn’t a new feature even though that quote kinda sounds like it is.
I was processing compressed .jsonl files recently (JSON lines format). I found that lzma gave a much better compression than gzip or bzip2, which helps for archival costs, but it's challenging to work with as software support is lacking. I do duckdb processing which supports gzip transparently. There's an extension for bzip2, but not for lzma or bzip3.
I ended up using gzip because it's best supported by the software I use and most likely to have support in software I adopt. But it gave the worst compression results of the options I tried. These bzip3 numbers certainly give me FOMO...
For that type of structured data (logs and such), a custom dictionary can be extremely effective. Zstd among others support generating a custom dictionary. You just run zstd --train over the data first, and then feed that in when you run zstd. For example: I found ~10 gigabytes of Usenet headers compress to ~700 MB using Zstd and 1 MB shared dictionary -- and that's with each header individually compressed, so o(1) lookup time.
Back in my data hoarder days, I downloaded one of those torrents that had all the world's books in it. It was dunno how many terabytes, but way more than I had HDDs.
So I stripped out formatting, got rid of dupes, and tried out zstd, which was the hot new thing, along with the dictionary feature you describe, figuring it'd help. It didn't. I tried having one per book, one per multiple books, one for the whole archive.
It didn't work, or the gains were so marginal that I ended up scrapping the approach.
So it's not impossible that it can work, but stuff like regular json already compresses extremely well, I haven't found a scenario where it's a major boon.
zstd is the go-to compression format these days. It's even supported in low-level software such as many linux filesystems.
I don't know much about duckdb but it looks like it supports zstd too: https://duckdb.org/docs/lts/data/json/loading_json
The thing zstd got really right is fast decompression. For write-once read-never data like backups lzma (aka xz/7zip/lzip) is great. But it takes forever to decompress. On zstd I can get good compression while decompressing the file only marginally slower than reading the uncompressed file from SSD
Writing your files directly into a compressed stream and decompressing on the fly has become almost a standard workflow for any files I'm going to read and write sequentially anyways. No need for the data to ever exist uncompressed on the file system. Previous formats never did that for me because they either had too much overhead or too little gain, often both
Agreed! Relatedly: https://news.ycombinator.com/item?id=49599953
How did I miss zstd?
Here are my benchmarks for 2.3 GB of jsonl, on a laptop. Compressed size, compress time, decompress time; using defaults.
At what levels? There’s no guarantee that the default compression level is comparable. You have to normalize by time spent compressing.
zstd with better compression level would be nice - these numbers are not really comparable since both time and compression level are too different
all hail zstd, the one format to rule them all
Not really, it's a popular dictionary-based compression format.
I'm pretty new to choosing compression libraries - I started with zlib and was delighted at how much faster and smaller zstd made things.
Since we kind of need a default "Need to compress something? Use this!" setting - would you prefer zlib over zstd, or something else for that role?
”Not really" what?
It's hard to understand what point you're trying to make. Can you clarify?
It isn't really the go-to compression format, because it isn't ubiquitous like gzip and zip, there are a variety of compression tools out there for different purposes, and there is image/audio/video compression. There is also specialized compression like what git does with its rolling hashes. I think of it as there not being a go-to compression format.
I think you're being a bit pedantic.
A go-to thing means it's a sensible default choice and has no little to no downsides (versus not using compression), it doesn't mean it's the best for everything.
Until now the go-to has been DEFLATE (gzip and zip) but zstd is definitely competing against it because it is better in almost every way.
For structured logs and json I've found a lot of success with PPM-style schemes.
If your JSON file has many of the same object, you could see ratios in the single digits.
I'd recommend trying openzl for jsonl.
The benchmarks are disingenuous, to the point of looking cherry-picked. The block size for bzip3 is set to 512MB, but the window size for zstd is left to its default (8MB I believe for high levels). So in this corpus, which is made up of all versions of Perl source code concatenated, the window is too small to see all the identical files and just match them. Also corpora made out of very long repetitions are pretty much the best case scenario for BWT-based compressors.
If we match the window size of zstd to that of bzip3 we get dramatically different results:
Almost 15x smaller than the baseline, and more than 2x smaller than bzip3, also CPU time halves (since long matches are found earlier, so there's less work to do).(the baseline number is slightly different because I don't have the exact Perl version set used by the author)
Also, in the benchmarks using lrzip, which would make the window size less relevant, zstd is not even compared.
> 8MB I believe for high levels
Yep, i found it in the source here:
- https://github.com/facebook/zstd/blob/d9c0c7e2cf8a8bf9fb98d3...
- https://github.com/facebook/zstd/blob/d9c0c7e2cf8a8bf9fb98d3...
Also, zstd docs say:
> Note: If windowLog is set to larger than 27, --long=windowLog or --memory=windowSize needs to be passed to the decompressor.
That always seemed annoying to me. They couldn't allocate 5 more bits somewhere to let the decompressor autodetect longer window sizes?
> That always seemed annoying to me. They couldn't allocate 5 more bits somewhere to let the decompressor autodetect longer window sizes?
I believe this is just to prevent the decompressor from arbitrarily blowing up memory usage based on the input; I think if you want to accept long windows you can just always decompress with --long=63 regardless of whether the input needs it? (you will run out of RAM decompressing a long=63 file though of course)
> They couldn't allocate 5 more bits somewhere to let the decompressor autodetect longer window sizes?
It's actually 8 bits: https://www.rfc-editor.org/rfc/rfc8878.html#name-window-desc...
These command line parameters change the maximum the decompressor will allow. It's 128 MiB by default in the command line decompressor; other uses (like the "zstd" content coding for HTTP in web browsers) use a lower limit of 8 MiB (see https://www.rfc-editor.org/rfc/rfc9659.html).
2^27 is 128 megabytes. How much RAM do you want the decompressor to have to allocate for every file? Especially since you can't tell, by looking only at the file size of a compressed file, how many bytes it will decompress to. You could read the file header, but if it's a malicious "zip bomb" type of file, the header could be lying.
I just tried a tar file of a git clone of the linux kernel sources where the most recent commit is 72c395024dac5e215136cbff793455f065603b06 (early Feb of this year). zstd -19 got a slightly smaller size (3582930348 bytes vs bz3 -b 511's 3597411687 bytes or 0.4% advantage to zstd). More significantly 4-core zstd decompression was 2.05 seconds vs a whopping 297 seconds for bzip3 -dj4 - 145x or over 2 orders of magnitude slower (about as much time to decode as to encode in the first place). bzip3 1.5.3 compiled with gcc-16.1.0. Granted, the .git objects are all compressed already and uncompressed tar-ball was only 5426667520 bytes, but even so...A lot of people care about fast(-ish) decompression. Maybe I did something wrong? Maybe `rm -rf .git` first would be a better benchmark?
How does memory usage compare between your two runs?
The benchmarks report 687M for their run of zstd, and 12178M and 18301M for the two runs of BZip3. Which itself is a bit eyebrow raising
This was my point too, but related to LZMA(2?) / xz, as the exact parameters were not specified while it supports setting compression level up to -9e, and the dictionary size can be controlled directly as well (in addition to quite a lot of fine-tuning knobs), increasing it up to 1536 MiB.
Nice catch.
it has been a long time since: "lies, damn lies, benchmarks" failed to hold true. Sometimes I wonder why gaming benchmarks has become so common.
Wow, that is widely disingenuous, I don't really think there is any excuse for that, I don't believe someone deep in compression algorithms wouldn't know they could adjust the block size, and 512GB is a huge block size for bzip3, as it needs to basically all be in memory so you can't pretend that's just 'the standard value'.
> 512GB is a huge block size for bzip3
Sorry! That was a typo, it should have been 512MB (now fixed). Still huge.
Can you tell me what the zstd invocation is that corresponds to the default invocation of bzip3, which uses block size 16 MiB (according to the man page)?
I got some really good results with bzip3 compression Wikipedia XML dumps, and I would like to check if it's actually better or if I was just calling zstd wrong.
If you want a 16MB window, use `--long=24` (2^24 is 16M). (I believe this is larger than the default window for zstd level 3, but smaller than the default window at higher compression levels.)
> However, the complexity of the algorithms, and, in particular, the presence of various special cases in the code which occur with very low but non-zero probability make it impossible to rule out the possibility of bugs remaining in the program.
Sounds like perhaps a nice testcase for formalization + AI?
It's beyond me why such foundational libraries don't have formal correctness proofs attached these days.
imo, partially because it's still not easy (in terms of code -> formal proof). For AI -- I've been Lean-ifying a simpler (but non-trivial) algo. Pointing (current) AI at it only goes so far and in fact might go "too far" in certain cases, where a non-formalized argument would have sufficed. There's also "who watches the watcher" -- did it really prove what we're supposed to prove?
For something like these compression algos, though, I imagine it would be much easier since they already have actual proofs out there.
I think this should include benchmarks zstd with larger windows and long range mode. I wouldn't be surprised if the window they used is smaller than an individual version tar file, which would prevent useful compression.
“Additional benchmarks on the same dataset” (2025) explores various compression levels with and without long range mode: https://news.ycombinator.com/item?id=42901476
For data recovery of archival stuff it's better to keep it uncompressed, no?
An interesting unintentional benchmark is to go to https://github.com/iczelia/bzip3/releases and see to what degree bzip3 compresses its own release archives; and go to https://github.com/iczelia/bzip3/blob/master/.github/workflo... to see what options have been chosen for the other compressors here.
It's distasteful to use such a name when it's not created by the bzip authors. For some reason open source developers love using would be trademark infringing names instead of coming up with something unique.
I would be interrested in a comparison with openzl
That's like comparing apples to pears. OpenZL is not general purpose. You specify a format for data and it compresses that format. Specifying a general "could be anything" format would be interesting, but I doubt it would compress as well.
"DO NOT COMPRESS ANY DATA WITH THIS PROGRAM UNLESS YOU ARE PREPARED TO ACCEPT THE POSSIBILITY, HOWEVER SMALL, THAT THE DATA WILL NOT BE RECOVERABLE."
So why would anybody, hobbyist or enterprise, use this? Or does something older like 7zip also have this caveat that I've never experienced.
This big warning gave me pause, too. Why not have a compression option that automatically checks the data after compression (by decompressing and checking against a hash of the original data), which would reduce the probability of undetected errors to that of a hash collision? i.e. like `7z a` followed by `7z t`, but in one command.
Is that all that different than the standard MIT License:
> THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE....
Practically, no. But that specific disclaimer could lead on to think that there may have been some observed data corruption in practice that isn't disclosed. I have no idea if there is, but I'm not keen to discover it myself.
Also practically, this isn't MIT. It is LGPL 3, which I believe includes the warranty terms of GPL 3, i.e., no warranty. So we're in the same place anyway.
Why LGPL when the original license is more permissive? (https://sourceware.org/bzip2/manual/manual.html)
The author of bzip3 probably doesnt like pushover licenses so made user rights stronger
bzip3 is not made by the same author as bzip2, that's why there is a licence disparity.
Feels pretty odd to take something named foo2 and claim foo3 on top of it.
Please stop questioning people's choice of license.
If you don't like it, you're entitled to not using it.
Any relation to Iczelion from the masm32 tutorial?
Those tutorials are about as old as the author of the repository.
Bro just decompile agiannis_text
Imagine bzip4
The latest release is a year ago, the last commit is two months ago, and the build is failing.
The claim “stronger than bzip2” is strange. What does it even mean?
Also, comparing parallel decompression benchmarks with bzip2 instead of pbzip2 seems unfair.
Depends - if parallel decompression of any bzip3 archive is possible I'd consider it fair, if it requires special flags on archive creation I'd consider it unfair. I didn't see any description about that on that page.
pbzip2 only can do parallel decompression on archives created with pbzip2, otherwise it'll fall back to single thread. There nowadays seems to be lbzip2, though, which claims to be able to add SMP support for standard bzip2 archives.
I'll need to try that next time I'm working with large archives - I learned about the pbzip2 limitations the hard way last time I was shuffling around a few multi-10GB archives, and was trying to speed things up fully utilising my 32 core threadripper.
> pbzip2 only can do parallel decompression on archives created with pbzip2
Oh I didn’t know that.
“for fairness, the benchmarks have been performed using single thread mode” (2025) https://news.ycombinator.com/item?id=42902241
Isn't that XZ?
No. It is an unrelated algorithm.
It's a very strange algorithm completely different from most compression methods, that's what makes it interesting IMO. But it's probably not realistically competitive, since one needs to do more after the burrows-wheeler transform, and all that "more" has been ridiculously more optimized in zstd and other modern compression methods. Compressing bwt-transformed data is easier, but that doesn't mean it's easy to further than what's easy.
You're probably thinking of LZMA2.
Impressive compression benchmark. Four times smaller than z standard.
I have not experimented with bzip3 recently, but more than a year ago I have done many tests with it.
Initially I was extremely impressed with it, because in a lot of tests it succeeded to compress hard-to-compress files, like movies, and in many cases it demonstrated a much better compromise between speed and compression ratio than zstd, i.e. depending on the command parameters I could make it either compress better than zstd at similar compression/decompression speed, or compress/decompress faster at a similar compression ratio.
Alas, the initial extremely favorable conclusion was short-lived, because trying later bzip3 on other data files gave worse results than zstd.
So the final conclusion was that the performance of bzip3 was somewhat unpredictable, being highly data dependent. For some files it provided outstanding compression ratio or speed, but for others it was inferior.
The problem was that without doing a compression there was no way to guess whether a file would be among those preferred by bzip3 or by zstd or by xz.
So now I would use it only for a file for which I want maximum compression and which I would compress once and decompress many times, so I can afford a very long compression time, during which I would test multiple compression algorithms, including bzip3 and zstd, with multiple parameter choices, and I would eventually choose the one that offers the best compromise between compression ratio and decompression time, for that particular file.
It certainly is a competitive compression algorithm, but unless it has changed since I last tested it, you cannot guess for which files it would win the compression competition.
Would a multi-stream archive format make sense at this point? I.e. store several compressed streams in the same file and use heuristics to decide where each file (or portion of file) goes.
I think so.
But developing the heuristics for choosing the appropriate compression algorithm for a stream of data is likely to need a very long time for compression tests of a lot of diverse training data, similarly to the training of a specialized ML model that classifies patterns.
Such heuristics should provide not only algorithm selection, but also parameter selection, when given only some simple input, e.g. the relative importances of compression ratio, decompression speed and compression speed.
with zstd at level 16 with default params (dict size, ...). Serious compression starts at level 19 and with much higher dict sizes.
how is this an honest benchmark:
There is a comparison with "zstd -19" on the Silesia corpus, showing better compression ratio for bzip3 (47.2 vs 53MB) while being ~5 times faster (and using only half the memory).
Even if the examples are highly cherry-picked, it is quite suprising to me that such pareto-dominance is possible at all.
edit: Tested it myself and found that it often also does slightly worse than zstd -19 in compression ratio but faster (it was slower in one case on "uncompressible" input).
Compression performance vs "zstd -19" seems to depends a lot on actual input data in a very unpredictable way. I'd assume the benchmarks that they show are definitely somewhat cherry-picked.
having used zstd, it has terrible defaults, optimized for speed and low-memory. You need to change it's params (not just level and dict size) to get high performance.
probably somebody should use a coding agent to do auto-research to optimize params for each compression algo, while matching one fixed goal - time, memory or size
The benchmark is very rudimentary. It does not test different levels/settings apart from its own -b 256/512 (does it affect decompression?), it doesn't measure compression time and memory usage. It does not specify parallel vs single-threaded (it mentions parallel on the one decoding number but what about the others?).
The lrzip test is interesting but it omits for example zstd and doesn't even have (de-)compression timings.
A lot more numbers are needed to present a fair and informative comparison.
I don't want this to be a swipe against bzip3, I only want to point out the presented benchmarks could be a lot better.